4 offensive players must line up on the line of scrimmage. 3 defensive players has to be down linemen (in a three of four-issue stance). A person linebacker might blitz on both aspect of the center. Defensive linemen will have to line up no wider than shoulder to shoulder ("shading") https://leisurecityguide.wordpress.com/2024/08/29/the-thrills-and-benefits-of-indoor-football/